It has previously been shown that high efficiency concentrator solar cells of Si and GaAs can be realized.
An article, "The V-groove Multijunction Solar Cell", by Terry I. Chappell published in IEEE Transactions on Electron Devices, Vol. ED-26, No. 7, July 1979, describes a type of silicon photovoltaic converter which has been termed a V-Groove multi-junction solar cell. A related U.S. Pat. No. 4,200,472 to Terry I. Chappell et al filed June 5, 1978 and issued Apr. 29, 1980, provides similar disclosure of technology. The solar cell consists of an array of many individual diode elements connected in series to produce a high voltage, low current output. All the elements of the cell are formed simultaneously from a single wafer by V-groove etching. Based on results of detailed simulations by computer, a conversion efficiency is predicted in excess of 24% for this cell when it is operated in sunlight after it has been concentrated approximately 100 or more times. The advantages of this cell over other silicon cells include: capability for greater than 20% conversion efficiency with only modest bulk carrier lifetimes, a higher open-circuit voltage, a very low series resistance, a simple one-mask fabrication procedure, and excellent environmental protection provided by a front surface of glass.
U.S. Pat. No. 4,128,133 shows a solar cell configuration with a flat III-V direct bandgap cell on one side of an insulating substrate and a flat IV direct bandgap cell on the other side.